This application relates to a blood culture sensor station which directs two sources of light into a blood culture specimen, measures the reemerging light from both light sources, calculates a ratio based on the two reemerging lights, and determines whether the specimen includes bacteria based on the calculated ratio.
Typically, the presence of bacteria in a patient's body fluid is determined by injecting a small quantity of body fluid (usually blood) into a vial which contains a culture medium. Various types of instruments are utilized to monitor changes in the carbon dioxide content of the vial. Carbon dioxide is a metabolic by-product of bacteria growth, and thus an increase in carbon dioxide in the vial indicates the presence of bacteria in the patient's body fluid.
Sensors have typically been inserted into the vial to test the carbon dioxide content. These so-called invasive sensors are somewhat undesirable due to the risk of cross-contamination. Non-invasive sensor systems have been developed which utilize chemical sensors disposed inside the vial. Typically, such sensors respond to changes in the carbon dioxide concentration by changing color, or by changing their fluorescent intensity. To monitor changes in the known chemical sensors, the systems have typically required one light source, one spectral exitation filter, one emission filter and one photodetector arranged adjacent to each vial. Each of these components must have extremely narrow specification tolerances to avoid substantial station to station sensitivity variations. However, even if it were possible to equalize all of the vial stations, certain lot-to-lot variations in the chemical sensor composition and certain vial-to-vial geometry variations may remain. Thus, the accuracy of such system is sometimes in question.
Some disadvantages of intensity based sensors can be overcome by utilizing fluorescent sensors which change fluorescent lifetime with changing pH, carbon dioxide concentrations, oxygen concentration, or other parameters. Such fluorescent lifetime sensors typically require expensive equipment. Further, color changing or fluorescent chemical sensors have typically required a certain temperature adaption time before a first vial test can be performed. Thus, a test cannot be made immediately upon receiving a vial when utilizing known chemical sensors.
It has been proposed to direct a light source into a vial, and monitor the reemerging light over time. It has been shown that increased carbon dioxide in a specimen will affect the reemerging light. The reemerging light can be evaluated to make a prediction as to the presence of bacterial growth in the vial. Problems remain with such proposed methods. If there is an unusually large amount of specimen within the vial, the medium within the vial may be more opaque than with a lesser amount of specimen. This would in turn effect the reemerging light. For that reason with known light based sensor systems, the amount of specimen within the vial can vary the accuracy of the test. Further, such light based systems do not allow immediate testing upon receipt of a vial.